Air conditioning apparatus



April 26, 1960 Filed Dec. 3, 1955 E. J. BURKE AIR CONDITIONING APPARATUS 2 Sheets-Sheet 1 INVENTOR.

EDWARD J. BURKE.

ATTORNEY.

April 26, 1960 s. J. BURKE AIR CONDITIONING APPARATUS Filed D80. 3, 1956 FIG. 2

INVENTOR. EDWARD J. BURKE.

ATTORNEY.

2 Sheets-Sheet 2 AIR CONDITIONING APPARATUS Edward J. Burke, North Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Application December 3, 1956, Serial No. 625,889

3 Claims. (Cl. 257-274) This invention relates to air conditioning apparatus including a refrigeration system which can be operated under the reverse cycle principle to provide either cooling or heating.

There is a class of air conditioning apparatus employing a refrigeration system which is capable of operating on the reverse cycle principle so that it can produce either cooling or heating, as required. However, when the refrigeration system has its cycle reversed to provide heating, it is sometimes incapable of providing adequate heating in regions where low temperatures are encountered. Consequently strip heaters are built into the air conditioning apparatus and are selectively utilized to supplement the heating capacity of the refrigeration equipment itself, as required. The heat exchange coil of the refrigeration system which supplies the cooling States Patent or heating is positioned next to a fanwhich induces air to be conditioned through it. The strip heaters also are positioned so that the fan will cause air which is to be heated to flow through them. If for any reason the fan should cease to operate while the strip heaters remain in operation a concentration of heat within the apparatus might create a fire hazard because the heat thus produced cannot be adequately dissipated.

It is therefore the chief object of this invention to provide an air conditioning apparatus employing strip heaters which can be operated safely.

lt is another object of this invention to provide an improved control for air conditioning apparatus employing a strip heater which will cause the strip heater to cease operation if the means utilized to dissipate heat therefrom is rendered inoperative.

A furthere object of this invention is to provide an interlock between the strip heater and the fan of an air conditioner which will deenergize the strip heater upon deenergization of the fan and thus obviate the possibility of a fire starting within the apparatus. Other objects will become readily apparent hereafter.

The present invention relates to air conditioning apparatus of the type including a refrigeration system which is selectively operable to cool or heat air. The refrigeration system includes a compressor, a first heat exchange coil, an expansion member and a second heat exchange coil, said elements being connected in series as enumerated, to form a refrigeration circuit. The first coil acts as an evaporator when the system is used for cooling. Also incorporated into the refrigeration circuit is a valve which, when properly set, causes the flow in a portion of the refrigeration circuit to be reversed so that the first coil which functions as an evaporator during the cooling cycle acts as a condensing coil during the heating cycle. However, it often happens that the first coil cannot provide adequate heat when low temperatures are encountered. Therefore strip heaters are provided to cooperate with the first coil to supplement the heat produced by it. A fan is positioned relative to the first coil and strip heaters so that it causes air to flow across them and thus be heated. An interlock is opera- 2,3i,323 Patented Apr. 26, 1959 ice might exist due to the strip heaters functioning when the heat produced thereby cannot be dissipated by the fan associated with them. The present invention will be more fully understood when the following specification is read in conjunction with the accompanying drawings wherein:

Figure 1 is a schematic diagram of the air conditioning apparatus which includes a reverse cycle refrigeration system; and

Figure 2 is a schematic wiring diagram of electrical circuitry which is used to control the air conditioning apparatus of Figure 1.

In Figure l, a compressor 10 is shown which compresses a suitable refrigerant and forces it through line 11 to conventional four way valve 12. In the position shown, valve 12 causes the compressed refrigerant to pass through conduit 13 therein and then to line 14 which leads to heat exchange coil 15. An electric fan 16 is juxtaposed relative to coil 15 for forcing air across it. When the valve 12 is in the position shown, heat exchange coil 15 functions as a condenser, and the refrigeration system is operating on a cooling cycle. The condensed refrigerant is then passed through line 17, check valve 18, line 19, line 20, expansion member 21 (which is preferably an expansion valve) and then through heat exchange coil 22. When the refrigerant flow is in the above-described path, coil 22 functions as an evaporator. An electric fan 23 which is juxtaposed relative to coil 22 induces air to be cooled through this coil and forces this air into the room to be cooled. A line 24 is connected to heat exchange coil 22 and passes the refrigerant back to four-way valve 12. In the position shown in the drawing, the refrigerant is caused to pass through conduit 25 of valve 12. It then passes through line 26 to the inlet side of compressor 10. The foregoing cycle is then repeated.

It is to be again noted at this point that when the refrigerating circuit operates in the above described manner, its function is to cool air. However, when it is desired to use the refrigeration circuit on a reverse cycle to provide heating, the flow of refrigerator is reversed through a portion of the circuit by manipulating fourway valve 12 and causing conduit 13 thereof to become in the foregoing manner, the heat produced in heat exchange coil 22 is caused to heat air which is induced through it by fan 23. It can readily be seen from Figure 1 that the solid arrows depict the direction of flow of the refrigerant when the system is used for cooling, and the dashed arrows depict the direction of flow of the refrigerant when the system is used for heating.

As can be seen from the foregoing description, there are expansion members 21 and 30 associated with heat exchange coils 22 and 15, respectively. These expansion members, which are'thermal expansion valves in this instance, and may be of any other suitable type which is known to the art, operate as such only when the heat exchange coil with which they are associated functions as an evaporator. To this end a check valve 28 provides a path for flow of refrigerant in the direction of the arrow 28 so that the refrigerant by-passes expansion member 21 when coil 22. acts as a condenser, the expansion function being performed by expansion member 30 through which the refrigerant is forced because check valve 18 associated therewith prevents the refrigerant from passing through the conduit in which the latter is placed. In an analogous manner, when the refrigerant flow is in the direction of the solid arrows so that coil 22 is acting as an evaporator, the refrigerant passes through the conduit in which check valve 18 is located (and thus by-passes expansion member 30) but is prevented from passing through the conduit in which check valve 28 is located and is thus forced to pass through expansion member 21. The purpose of the foregoing arrangement is to have the actual expansion of refrigerant in the member which is associated with the heat exchange coil which is performing the function of the evaporator so that the cooling which is obtained from the expansion of the refrigerant in the expansion member does not produce cooling which minimizes effective heat exchange with the air being conditioned as, for example, would occur ifthe expansion took place in coil 21 whenheat exchange coil 22 was being used as a condenser.

As noted above, the refrigeration system is frequently incapable of providing suflicient heating, especially when it is used in areas which are subject to low temperatures. A strip heater 31 is therefore provided (as explained in detail hereinafter) which consists of a suitable high resistance wire through which current is adapted to be selectively passed to provide heat. Thus the air which is heated to a certain degree by being induced through heat exchange coil 22 by fan 23 is further heated by being forced through strip heater 31 by said fan 23.

It can readily be appreciated that the above-described system can be a part of a window type room air conditioner, but is not limited thereto. If it should be used as a window type unit, heat exchange coil 22, fan 23, expansion member 21, and strip heater 31 are within the portion of the unit which is indoors, and heat exchange coil 15, expansion member 30, fan 16, and compressor are located outdoors. The preferred type of air conditioning unit in which the present system is employed is shown in the copending application of Edward J.

Burke, Serial No. 625,890, filed December 3, 1956, V

wherein the air conditioning portion of the system is located indoors and the remainder of the system is remotely located outdoors. It can thus be seen that the air conditioning apparatus of the present application is capable of wide application.

The controlcircuitryfor the system of Figure 1 is shown in Figure 2. A suitable source of three-phase current (not shown) is adapted to supply current via leads L L and L to the windings 32 of the motor (not shown) which drives compressor 10. It will be, of course, understood that the system can operate on single phase if it is suitably modified. The primary winding 33 of a transformer 34 is coupled across leads L and L and selectively induces a voltage in the secondary coil 35 of transformer 34 when the secondary circuit is completed. In this respect, it is tobe noted that the secondary circuit may be completed in one of two ways, through fan switch 36 or through master switch 37.

Under certain situations it may be desirable to operate indoor fan 23, Figures 1 and 2, to merely circulate air when the refrigerating system is not in operation. The arm 38 of fan switch 36 is therefore placed into contact with terminal 39 of fan switch 36. Thus a circuit is completed through secondary coil 35 by way of fuse 40', lead 40, lead 43, terminal 39 andswitch arm 38 of fan switch 36, lead 44, indoor fan relay coil 42, lead 41, and lead 45. This will cause relay arm 46 to contact terminal 47 of indoor fan relay 48 to pass current from lead L through lead 49, terminal 47 and relay arm 46 of indoor fan relay 4%, lead 50, indoor fan motor 23, lead 51, interlock relay coil 52, lead 53, to lead L thus completing a circuit which will cause indoor fan motor 23 to operate independently of the operation of the refrigeration system of Figure 1. However, under normal conditions, switch arm 38 of fan switch 36 is in the position shown in the drawing, and the fan 23 will not operate unless the refrigeration system is in operation.

In order to set the system in operation, master switch 37 is placed in cooling or heating position. Master switch 37'is a double pole-double throw switch having arms 54 and 55 which are mechanically coupled by linkage 56 so that they are either in contact with cooling terminals 58 and 59 of switch 37, respectively or with heating terminals 60 and 61 of switch 37, respectively.

When switch 37 is in the cooling position, that is, when arms 54 and 55 thereof are in contact with terminals 58 and 59, respectively, a circuit will be completed from secondary transformer winding 35, through lead 40, switch arm 54 and terminal 58 of switch 37, lead 62, thermostatic switch 63, lead 64, terminal 59 and switch arm 55 of switch 37, lead 65, compressor holding coil 66, normally closed switches 67, 68 and 69, lead 70, and lead 45 back to the other side of transformer secondary winding 35. When current is flowing in the foregoing path, compressor holding coil 66 is energized and causes four pole-single throw switch 71 to remain closed, as shown in Figure 2, for the purpose of supplying current to compressor motor windings 32. More specifically, current will flow from line L through contact 72 of switch 71, lead 73, fasttrip 74 (which may be a portion of the solder-pot or equivalent structure for disrupting the how of current if too great a current flow should exist), lead 75, motor winding 76, motor winding 77, lead 78, contact 79 of switch 71, and lead 80 to complete the circuit to line L Current will also flow from line L via lead 81, contact 82, fast-trip 83 (which is of the same construction as fast-trip 74), lead 84, winding 85, winding 77, lead 78, contact 79 and lead 80 to complete the circuit to line L .71 only if thermostatic switch 63 (which may be made of bi-metal) is closed to complete the circuit in the above described manner. Thermostatic switch 63 is responsive to the temperature of the room which is to be cooled. Thus, if the room temperature is at or below the desired temperature, thermostatic switch 63 will be open and the compressor 10 will be idle. On the other hand, if a high temperature exists, switch 63 will close to complete the foregoing circuit to relay holding coil and thus cause the compressor motor to be energized. A resistor 86 is placed in parallel with thermostatic switch '63, and acts as an anticipator in the sense that the flow of current :therethrough will generate a small amount of heat and this in turn will cause thermostat 63 to close to start up the compressor before the room temperature gets' too high. It is also to be noted that resistance 86 is of such amagnitude that it will cause a sufliciently high voltage droplwhen' thermotatic switch 63 is open so that holding coil 66 will not close switch 71.

As stated above, switches 67, 68 and 69 are placed in series in the line with compressor holding coil 66. Switch 67 is a high pressure cut-out switch which is suitably attached to the compressor or any other part of the high pressure side of the system and will open the circuit to compressor holding coil 66 if the compressor pressure exceeds a predetermined maximum. Switch 68 is a high Switch 69 is an overload switch whichmay cooperate with either fast-trip switch 74 or 83. If the flow of curi rent through the compressor motor winding 32 becomes too great, either fast-trip switch will cause switch 69 to open, thus-disrupting the flow of current to compressor holding coil 66 and causing switch 71 to open to shut down the compressor motor. Thus it can be seen that switches 67, 68 and 69 provide protection against damage due to malfunctioning of the compressor and compressor motor.

When the air conditioning apparatus is operating on the cooling cycle, indoor fan 23 and outdoor fan 16 are in operation. The indoor fan 23 is coupled between lines L, and L when the arm 46 of indoor fan relay 48 is closed by the how of current through fan relay coil 42 in the general manner described above when the operation of fan switch 36 was explained. However, when the refrigerating circuit is in operation, arm 38 of fan switch 36 is positioned in contact with terminal 88, the flow of current through relay coil 42 then being from the secondary transformer winding 35, via lead 40, through switch 37, lead 89, arm 38 of fan switch 36, lead 44, indoor fan relay coil 42, lead 41, and lead 45 to complete the circuit to secondary transformer winding 35. The outdoor fan 16 is caused to operate because there is a flow of current from line L lead 90, contact 91 of switch 71, lead 92, outdoor fan 16, lead 93, normally closed arm 94 of defrost relay 95, and lead 96 to complete the circuit to line L It can thus be seen that when the air conditioning apparatus is operating on the cooling cycle, the compressor is in operation, valve 12 is in the position shown in Figure 1, and indoor fan 23 and outdoor fan 16 are functioning.

When it is desired to use the air conditioning apparatus on the heating cycle, switch 37 is manipulated into the heating position so that arms 54 and 55 thereof are placed into contact with terminals 60 and 61, respectively. Coupled between contacts 60 and 61 is a heat thermostat 97 and resistance 98. Thermostat 97, which may be of the conventional bi-metallic type, is adapted to deflect and thus close the circuit between terminals 60 and 61 when the temperature of the room in which it is positioned falls below a given value. It can readily be seen that when heat thermostat 97 is closed that a circuit is provided through switch 37 which will cause compressor motor holding coil 66 to close switch 71 and also cause indoor fan 23 and outdoor fan 16 to operate, in the same manner as described in detail relative to the cooling cycle. However, in order to cause the air conditioning apparatus to supply heat, it is necessary to reverse the flow of refrigerant through the circuit of Figure 1. For this purpose a circuit is completed from transformer secondary winding 35, via lead 40, switch arm 54 and terminal 60 of switch 37, lead 99, relay coil 100 of four-way valve relay 10 1, lead 102 and lead 45 to complete the circuit to transformer secondary winding 35. The energization of four-way valve relay coil 100 causes relay arm 103 to be placed into contact with terminal 104. Thus a path is provided for the flow of current from line L through four-way valve relay arm 103, solenoid coil 104, lead 105, lead 93, normally closed defrost relay arm 94, and lead 96 to complete the circuit to line L When solenoid coil '104 is thus energized a suitable mechanical linkage 1% (associated therewith in the conventional manner) which is also coupled to four-way valve 12, will cause the latter to change its position so as to reverse the flow of refrigerant in the circuit, as described in detail above.

While the air conditioning apparatus may provide adequate heating in the foregoing manner when the temperature is not too low, it is necessary to supplement the heating it can produce when relatively low temperatures are encountered. For this purpose a strip heater 31 (Figures 1 and 2) is provided to selectively supplement the heat produced by the refrigeration system, as re Y I quired. As the temperature of the room being. heated drops below a predetermined value, heat thermostat 107 will close. Connected in series with thermostat 107 is outdoor thermostat 108 which will close only when the outdoor temperature drops below a certain value, for example 40 F. These two thermostats are in series in a circuit which is adapted to ultimately energize the strip heater 31. It will readily be seen hereafter that if either thermostat 107 or 108 is open, the strip heater cannot be energized. Also connected in series with thermostats 107 and 108 is normally closed overheat thermostat 109. If the strip heater 31, when operating, should cause too high a temperature to develop in the vicinity of thermostat 109, this thermostat will also open, thus ultimately breaking the circuit which energizes strip heater 31. Also coupled in series with the preceding thermostats is a strip heater relay coil 110, an indoor fan-strip heater interlock relay arm 111, and a time delay switch 112. The latter two must be closed before the strip heater 31 can operate, and the interlock relay coil 110 must be energized.

The strip heater energizing circuit operates in the following manner: As explained above, the setting of switch 37 on heat will cause a reverse flow of refrigerant through a portion of the refrigeration circuit, energize the compressor motor 19, and set indoor fan 23 and outdoor fan 16 in operation. However, it is undesirable that the strip heater 31 should be energized at the same time that the foregoing elements start operating because this would in all probability overload the circuit due to the starting surge of the compressor. Therefore, a time delay switch 112 is provided which will prevent the strip heater from being energized until a predetermined time interval has elapsed after the other elements of the circuit have been put into operation. It can be seen that when switch 71 is closed the compressor motor and the fans 23 and 16 will immediately start operating. At the same time there will be a flow of current from line L via lead 90, arm 91 of switch 71, lead 92, lead 113, coil 114, and lead 115 to complete the circuit to line L Coil 114 is a coil which will produce a small amount or" heat, and it is placed in proximity to time delay switch 112 which is thermostatic. As thermostatic switch 112 is heated up, it will contact terminal 116 and thus allow current to flow through strip heater relay coil 110 if certain other conditions are met, as discussed hereafter. Thus it can be seen that when the system is first started up on the heating cycle the strip heater 31 cannot possibly be energized until the other parts of the system are already in operation, and thus there cannot be any overloading of the circuit in this respect.

it is also to be noted at this point from Figure 1 that strip heater 31 is positioned near fan 23. If strip heater 31 was allowed to operate when fan 23 was not operating, there could be concentration of heat in the vicinity of strip heater 31 which could constitute a fire hazard. The circuitry of the present invention makes it impossible for strip heater 31 to operate unless indoor fan 23 is in operation. In other words, unless fan 23 can dissipate the heat produced by strip heater 31, the latter cannot operate.

The present circuit performs the foregoing function in the following manner: As noted above, whenever indoor fan relay coil 42 is energized during operation of the system, arm 46 of indoor fan relay 48 will contact terminal 47. Thus the flow of current through indoor fan 23 is from line L through terminal 47 and arm 46 of indoor fan relay 48, through the winding (not shown) of indoor fan 23, lead 51, interlock relay coil 52 and lead 53 to line L; to complete the circuit. Whenever current is flowing through the foregoing branch of the circuit, it must of necessity flow through interlock relay coil 52. When this is the case, indoor fan-strip heater interlock relay arm 111 will be in contact with terminal 117' to close this portion of the strip heater energizing, circuit. It can thus be seen that unless the indoor fan 23 is energized, there 7 cannot possibly be any current flow through coil 52, and consequently no energization of strip heater 31. Strip heater 31, Figure 2, is energized in the following manner: Heat thermostat 107, which is located in the room to be heated, must be closed; outdoor thermostat 108,'which is located outdoors and must sense a certain minimum outdoor temperature must be closed; overheat thermostat 109 must be closed, and is in this condition when there is not an excessive amount of heat in the vicinity of the strip heater 31; indoor fan-strip heater interlock relay arm 111 must be in contact with terminal 117, but it can only be in this condition when indoor fan 23 is in operation; and time delay switch 112 must be closed. When all of these conditions are met, there will be a flow of current from secondary transformer winding 35 via lead 40, arm 54, terminal 60 of switch 37, lead 118, switches 107, 108 and 109, strip heater relay coil 110, switches 111 and 112, and lead 45 to complete the circuit back to transformer secondary coil 35. When current is flowing through strip heater relay coil 110, strip heater relay arm 119 will be placed into contact with terminal 120, thus completing a circuit from line L via lead 121, strip heater 31, lead 122, terminal 120 and arm 119 of the strip heater relay, and via lead 123 to line L When the air conditioning system of Figure 1 is being used on the heating cycle, heat exchange coil 15, which functions as an evaporator and is located outdoors, may become coated with an insulating layer of frost which interferes with the proper operation of the system. Therefore a defrost control such as shown in the patent application of Richard H. Merrick, Serial No. 531,903, filed September 1, 1955, is incorporated into the system to eliminate objectionable frosting. Defrosting is effected by selectively reversing the flow of refrigerant through the refrigerating apparatus, and by thus causing the heat exchange coil 15 to function as a condenser, the frost formed on coil 15 will be melted. This is accomplished in the following manner: A timer motor 124, which can be a small synchronous motor, is coupled by leads 125 and 126 to lines L and L respectively. Motor 124 is connected by a suitable mechanical linkage 127 to a switch arm 128 which is intermittently brought into contact with terminal 129 as motor 124 rotates, a thermostatic switch arm 130 is positioned in the line which provides refrigerant to heat exchange coil 15. If the temperature of this line falls to a predetermined value which indicates the presence of frost on heat exchange coil 15, thermostatic switch 130 will close, that is, it will contact terminal 131. When switch arm 130 is in contact with terminal 131 and switch arm 128 is in contact with'terminal 129, there will be a flow of current from line L via lead 132, lead 133, defrost relay coil 134, lead 135, lead 136, defrost relay coil 134, switch arm 130, terminal 131, switch arm 128, terminal 129, and via lead 137 to line L When relay coil 134 is thus energized, relay arm 94 of defrost relay 95 will be in the open position. The flow of current through solenoid coil 104 will therefore be disrupted. This in turn will cause four-way valve 12 to return to a cooling cycle position because it is spring biased in this position. When this occurs the flow of refrigerant will be reversed so that outdoor heat exchange coil 15 will function as a condenser, and thus defrost will be effected.

It is undesirable that outdoor fan motor 16 should be operating during the defrost cycle, because it would then be blowing cold air over heat exchange coil 15, and it thus would be opposing the defrosting operation. Therefore outdoor fan 16 is deenergized during the defrost cycle by the opening of switch arm 94 of defrost relay 95, as explained above, because arm 94 links leads 93 and 96 which are necessary to complete the circuit to outdoor fan 16.

Whenever the air conditioning apparatus is placed on a defrost cycle, indoor heat exchange coil 22 functions as an evaporator, and thus inherently produces cooling. However, it is undesirable to have cool air presented to a room which requires heat. In order to minimize the effect ,of the cooling thus produced, the defrost relay causes the strip heaters to function during the defrost cycle, and they in turn counteract the cooling produced by heat exchange coil 22 during defrost. As can be seenfrom Figure 2, leads 133 and 135 are coupled to defrost relay coil 134" which is energized whenever the defrost cycle is in operation, as explained in detail above. When relay coil 134" is energized it will cause relay arm 138 to contact terminal 139. Thus a circuit is completed across the transformer secondary winding 35 through lead 99, relay coil 100, lead 102, lead 140, switch arm 138, lead 141, switch arm 109, coil 110, and switches 111 and 112. It can thus. be seen that this circuit by-passes heat thermostat switch 107 and outdoorthermostat switch 108. Therefore strip heater relay coil 110 will be energized to close the strip heater circuit whenever the apparatus is being defrosted on the heating cycle regardless of whether the strip heaters were previously required to be in operation because of the action of switches 107 and 108. It is also to be noted at this point that the strip heater 31 cannot possibly be energized unless the indoor fan 23 is in operation, as explained above.

It is to be noted at this point that the defrost relay coil has been presented on the drawing as consisting of coils 134, 134' and 134" for the sake of ease of description. However, it is to be understood that in actual practice coils ,134, 134' and 134" may be a single member.

' As explained above, defrost timer motor 124 closes switch arm 128 intermittently. However, once the defrost cycle has started, it does not stop until the defrosting has been completed regardless of whether switch arm 128 is opened or closed, the stopping of the defrost cycle being dependent on the opening of thermostatic switch arm 130. To achieve this mode of operation, a latching relay switch 142 is utilized. Once current is flowing through defrost relay coil 134', switch 142 will close. Thus, as long as current is flowing through defrost relay coil 134, relay arm 142 will remain closed to perpetuate the flow of current through coil 134' via leads 143 and 144.

I While I have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In air conditioning apparatus of the type including a refrigeration system operable to selectively heat or cool air, the combination of a compressor having an inlet and an outlet, a motor for actuating said compressor, first and second heat exchange coils normally coupled to said compressor, inlet, and outlet, respectively, when said apparatus is used for cooling, expansion means coupling said coils to each other, valve means coupled between said coils and said compressor for causing said first and said second coils t9 be coupled to said compressor, outlet. and inlet, respectively, when said apparatus is used for heating, a strip heater mounted proximate said first coil for supplementing the heat produced by said coil, a fan mounted proximate said strip heater, means for energizing said motor and said fan and means for energizing said strip heater connected to said means for energizing said motor and said fan, said strip heater energizing means including an indoor thermostat, an outdoor thermostat, an overheat thermostat, a strip heater relay coil, and an interlock relay arm placed in series, an interlock relay coil associated with the interlock relay arm and .a strip heater relay arm, energization of the interlock relay coil when the fan is energized closing the interlock relay arm to energize the strip heater relay coil to close the strip heater relay arm thus energizing the strip heater when said thermostats are closed and deer:- ergization .of the fan deenergizes the interlock relay coil opening the interlock relay arm to deenergize the strip heater relay coil to open the strip heater relay arm thus deenergizing the strip heater.

2. Air conditioning apparatus according to claim 1 in which a time delay switch is placed in the heater energizing means in series with the strip heater relay coil and the interlock relay arm, and a heater coil is associated with the time delay switch, said time delay switch and the heater coil cooperating to prevent energization of the strip heater until a predetermined time has elapsed after the fan has been placed in operation.

3. Air conditioning apparatus according to claim 2 having means for defrosting the coil employed as the evaporator of the refrigeration system during the heating operation.

References Cited in the file of this patent UNITED STATES PATENTS I-Iynes Feb. 12, Banfii Apr. 2, Qualley et al. Mar. 6, Ditzler et al. Mar. 23, Burgess Aug. 21, Biehn Sept. 17,

FOREIGN PATENTS Great Britain Oct. 13,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,934 323 April 26, 1960 Edward J. Burke It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 46 for "further-e" read further column 2, line 47, for "refrigerator" read refrigerant column 6 line 55 for "be concentration" read be a concentration Signed and sealed this 27th day of September 1960.

( SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

